Hydrogel fibers are promising carriers for biological applications due to their flexible mechanical properties, well-defined spatial distribution, and excellent biocompatibility. In particular, the droplet-filled hydrogel fibers with the controllable dimension and location of droplets display great advantages to enhance the loading capacity of multiple components and biofunctions. In this work, we proposed a new all-in-water microfluidic system that allows for one-step fabrication of aqueous-droplet-filled hydrogel fibers (ADHFs) with unique morphology and tunable configurations. In the system, the aqueous droplets with equidistance are successfully arranged within the alginate calcium fibers, relying on the design of the pump valve cycle and the select of two immiscible liquids with a stable aqueous interface. The architecture of the ADHF can be flexibly controlled by adjusting the three phase flow rates and the valve switch cycle. The produced ADHFs exhibit high controllability, uniformity, biocompatibility, and stability. The established system enabled the formation of functional human islet organoids in situ through encapsulating pancreatic endocrine progenitor cells within microfibers. The generated islet organoids within droplets exhibit high cell viability and islet-specific function of insulin secretion. The proposed approach provides a new way to fabricate multifunctional hydrogel fibers for materials sciences, tissue engineering, and regenerative medicine.
Keywords: all-in-water microfluidic system; aqueous-droplet-filled hydrogel fiber (ADHF); islet organoids; one-step fabrication; tissue engineering.